Familiarity Breeds Tolerance: the Development of Social Stability in Flocking Siskins (Carduelis spinus)

Abstract

Behavioural integration associated with the fusion of two flocks is analyzed in captive siskins (Carduelis spinus) by quantifying changes in social behaviour with time since joining. In general there was an increase in the incidence of tolerant behaviour, supplanting attacks and hopping withdrawals with time since fusion of the flocks. However, the number of displays and flights showed the opposite, negative, trend. Taking dominance status into account, the greatest change in behaviour with time since joining is an increase in tolerance by dominants of new flock companions. Factorial analysis of correspondences was used to study how different birds changed their behaviour with time since joining a flock. This analysis showed that the introduction of new birds did not disrupt relationships with familiar birds, and that residents are dominant in interactions with the incoming new flock companions. The analysis also demonstrated that relationships within the new flock had stabilized 20 days after the flocks had joined. The characteristics of the socially integrated group of siskins are quite similar to those described by Rohwer & Ewald (1981) in their shepherds hypothesis: dominants tolerate their subordinates feeding in close proximity, offering them a profitable feeding area, but also supplant them to obtain food; both dominants and subordinates benefit from being in a flock. As a consequence, constant changes of membership in flocks is costly not only because birds lose dominance status, but also the advantages of clear dominant and subordinate roles.

Prior residence effect in wintering male Eurasian siskins is not related to resource holding power

“…Since residency is not related to the black bib size, it is probably not either related to personality, and hence, the dominance of residents over transients is not expected to result from a behavioural syndrome but from a difference in prior residency. This is supported by the plasticity in social interactions among flock members of different groups joined together found in a previous study (Senar et al 1990a). Since resident and transient siskins differ in wing shape (Senar et al 1994), body mass regulation (Senar et al 2001) and vigilance (Pascual et al 2014), residency in Eurasian siskins is probably a polymorphic trait (i.e.…”

“…However, two other studies seem to support the dear-enemy effect. In the first study, it was found that the social relationships between a resident and an intruder group of siskins that were joined together stabilized after 20 days, with a high increase in tolerant behaviour between the members of both groups and a reduction in the dominance of prior residents over intruders (Senar et al 1990a). In the second study, it was found that transients interacted with other transients more often than expected and residents with other residents less than expected (Senar et al 1990b).…”

Familiarity adds to attractiveness in matters of siskin mate choice

“…To ensure familiarity between the three birds, they were retained in their same groups for at least two months over the winter, before starting the mate-choice experiments. Previous studies have determined that familiarity in siskins is attained after 20 days of cohabiting in the same cage [48]. Our period of at least two months is therefore more than sufficient time for the three birds to become familiar.…”

“…cardueline finches, like siskins, crossbills and citril finches, breed in semicolonies that have high social interaction among their members [80,82]. The high social costs of flock switching enhance membership stability [48,[83][84][85][86], and data on siskins and other finches suggest that flocks formed in the original breeding localities probably remain together in the wintering grounds [86]. In this scenario, if birds develop a mating preference for familiar birds, flock structure would favour pairing with individuals from the same breeding subpopulation, thereby reducing gene flow and allowing local adaptation.…”

Sex-specific aggression and sex ratio in wintering finch flocks: serins and siskins differ

“…As serins have a highly despotic social system (Senar et al 1997), we predicted that males would preferentially attack females, the subordinate fraction of the population. Conversely, as siskins display a feudal social system with like-vs-like aggression (Senar et al 1990a(Senar et al , 1997Ripoll et al 2004), we predicted that males would preferentially attack other males. We additionally predicted differences in sex ratios between the two species at the end of the winter.…”